Leber et al.: Influence of release season on size-dependent survival of Mugil cephalus 
271 
tory, tags were located and extracted with a field- 
sampling detector. Tags were decoded by using a bin- 
ocular microscope (at 40x). To verify tag codes, each 
tag was read twice (once each by two different re- 
search assistants). 
Data were analyzed with Systat (Wilkinson, 1990). 
A randomized-block factorial analysis of variance 
(ANOVA) was used to compare means. Systat Basic 
was used to write tag decoding algorithms. For each 
recaptured fish, the algorithms identified batch size, 
release date (lot), release site, size-at-release, and 
release season from the tag codes identified in the 
laboratory. An error-check algorithm was also writ- 
ten to help identify errors that may have been made 
in reading tag codes. Variance estimates are ex- 
pressed throughout as standard errors (with 
n=number of release lots). 
Results 
Tag retention 
Tag retention in 4,799 individuals subsampled and 
held in tanks for six months averaged 98.6% (0.4% 
SE). With one exception (92.4%), all retention rates 
within release lots exceeded 97%. No significant tag 
loss was observed in any group later than 1 month 
after tagging. This is a normal tag loss rate for coded- 
wire tags (Blankenship, 1990). 
Recapture summary 
Of the fish released, 2,511 cultured striped mullet 
were recaptured in monthly cast-net samples at nurs- 
ery habitats. Based on the 98.6% average tag reten- 
tion rate, the number of cultured fish recaptured can 
be extrapolated to 2,546, or 2.8% of the fish released. 
About 6.6% (166) of the tags taken from the 2,511 
recaptured fish were lost during extraction. 
Total number of tagged fish in samples decreased 
over the 11 -month monitoring (Table 3) but was fairly 
constant during the last 7 months of the study (when 
numbers of tagged fish ranged from 49 to 134 indi- 
viduals). Total number of tagged fish collected was 
greater at Kaneohe Stream. However, this pattern 
varied considerably from month to month, and most 
of those fish were collected within 1 month after the 
May and July releases. 
Tagged fish represented between 8% and 48% of 
the striped mullet captured in monthly samples (from 
all stations combined; Table 3). Percentage of cul- 
tured fish in samples was greatest at Kaneohe 
Stream, where contribution rates declined from 76% 
following the May release to 41% by the end of the 
study. Although numbers of tagged fish collected at 
Kahaluu Stream were often similar to those for 
Kaneohe Stream, there were always greater numbers 
of wild fish in collections at Kahaluu Stream (Table 3). 
Impact of release season 
Recapture rates and contribution rates When size- 
at-release was not considered, the contribution of 
cultured fish to recruitment appeared to be unaf- 
fected by release season. Release season had no sig- 
nificant effect on mean recapture rates over time 
(ANOVA, P>0.54, data from all size-at-release inter- 
vals combined). After 3 months in the wild, mean 
numbers of cultured fish in samples varied between 
Table 3 
Numbers of wild and hatchery-released striped mullet, Mugil cephalus, recovered in cast-net samples made in Kaneohe Bay. 
Proportions of hatchery fish were determined by the presence of a coded wire tag. 
1991 1992 
Standard 
Collection site 
Source 
May 
Jun 
Jul 
Aug 
Sep 
Oct 
Nov 
Dec 
Jan 
Feb 
Mar 
Total 
Mean 
Error 
All stations in 
Wild 
985 
1,099 
1,439 
453 
659 
722 
952 
550 
824 
864 
310 
8,857 
805.2 
95.7 
Kaneohe Bay 
Hatchery 
912 
194 
551 
184 
101 
117 
134 
76 
116 
77 
49 
2,511 
228.3 
79.9 
% Hatchery 
48.1 
15.0 
27.7 
28.9 
13.3 
14.0 
12.3 
12.1 
12.3 
8.2 
13.6 
18.7 
3.5 
Kahaluu Stream 
Wild 
265 
201 
303 
137 
260 
318 
331 
158 
350 
184 
134 
2,641 
240.1 
24.3 
(Release site in 
Hatchery 
184 
122 
237 
25 
20 
56 
91 
25 
46 
15 
18 
839 
76.3 
22.7 
N. Kaneohe Bay) 
% Hatchery 
41.0 
37.8 
43.9 
15.4 
7.1 
15.0 
21.6 
13.7 
11.6 
7.5 
11.8 
20.6 
4.1 
Kaneohe Stream 
Wild 
207 
87 
264 
88 
44 
85 
115 
52 
85 
87 
41 
1,155 
105.0 
20.9 
(Release site in 
Hatchery 
653 
64 
270 
135 
43 
52 
35 
45 
55 
45 
28 
1,425 
129.5 
56.5 
S. Kaneohe Bay) 
% Hatchery 
75.9 
42.4 
50.6 
60.5 
49.4 
38.0 
23.3 
46.4 
39.3 
34.1 
40.6 
45.5 
4.2 
